PONDPOISE
Goldfish, koi & the calm of a well-kept pond — stocking, filtration, and care.
From sizing a new pond and checking stocking density to sizing a filter, working out a feeding amount, planning a water change, and buying the right liner, PondPoise pairs free hands-on calculators with clear pond-keeping guides. Fewer surprises, healthier fish.
Pond Calculators & Tools
Free tools for every pond — pond volume calculator, fish stocking density calculator, filter turnover calculator, feeding amount calculator, water-change calculator, and pond-liner size calculator.
Pond Volume Calculator
Work out how many gallons or litres your pond holds from its shape and dimensions — rectangular, round, oval, or an irregular naturalistic shape
Fish Stocking Density Calculator
Check your total fish length against your pond volume to see whether it's comfortably stocked, crowded, or has room for more
Filter Turnover (GPH) Calculator
Convert your pond volume and a target turnover time into the pump flow rate, in gallons per hour, your filtration needs to keep up with
Feeding Amount Calculator
Scale a daily feeding amount to your fish's total weight and the water temperature
Water Change Calculator
Work out exactly how much water to remove and replace for a given percentage change
Pond Liner Size Calculator
Size the liner sheet you need to buy from your pond's length, width, and depth, before you break ground
Goldfish & Koi Museum
Wander an immersive, richly illustrated collection — the many varieties of goldfish, the patterned koi bred for centuries in Japan, the other ornamental fish suited to a garden pond, and the water gardens they live in, each in its own gallery. Every entry, image, and fact is drawn from Wikipedia and Wikimedia Commons.
Tour the museum →From the Journal
Clear guides on pond setup, stocking, filtration, feeding, water quality, and pond liners — reading to pair with the calculators above.
How Big Should Your Goldfish Pond Be? A Volume & Sizing Guide
Volume is the number every other pond decision depends on. Here's how to think about size, depth, and shape before you dig, with a worked example.
Goldfish vs Koi: Which Pond Fish Is Right for You
Goldfish and koi look similar at a glance but differ enormously in size, space needs, and lifespan. Here's how to decide which one fits your pond.
How Many Fish Can Your Pond Actually Hold? Stocking Density Explained
The gallons-per-inch rule is the standard way to check stocking density. Here's what it means, where it comes from, and what can shift it.
Pond Filtration 101: Choosing the Right Pump and Turnover Rate
A pond filter's job is to keep up with your fish's waste. Here's how mechanical and biological filtration work, and how to size a pump correctly.
What and How Much to Feed Goldfish and Koi Through the Seasons
Goldfish and koi are cold-blooded, so feeding needs to track water temperature through the year, not a fixed daily routine. Here's how.
Water Changes 101: How Much, How Often, and Why It Matters
A running filter doesn't remove everything from pond water. Here's why partial water changes are still necessary, and how to size one correctly.
Keep Learning
Plain-language explainers on the building blocks of pond-keeping — getting a pond set up, choosing what to stock it with, keeping the water clear, feeding through the seasons, and putting it all to work in the world — everything you need to go deeper with confidence.
Visit the Learn hub →